1. Field of the Invention
This invention relates to a magnetic memory device, more particularly to an arrangement of write lines of a magnetic memory device and a decoding method.
2. Description of the Related Art
A memory cell using the TMR (Tunneling Magneto Resistive) effect of a magnetic random access memory (MRAM) is composed of, for example, an MTJ (Magnetic Tunnel Junction) element and a select transistor. One end of the select transistor is connected to the MTJ element and the other end thereof is connected to a ground line. Information is written into the MTJ element by applying a synthetic magnetic field produced by the bit line and the word line to change the direction of the relative spin of two ferromagnetic films.
The direction of the spin of the ferromagnetic film of an MTJ element is commonly changed by a synthetic magnetic field generated by a bit line and a word line crossing at right angles with the MTJ element sandwiched therebetween. U.S. Pat. No. 6,714,445B2 discloses a writing method which uses not only bit lines and word lines but also third write lines crossing neither the bit lines nor the word lines at right angles. Generally, a variation in the size of the shape of the asteroid curve, the distortion of the shape, and misalignment, and other conditions occur among a plurality of MTJ elements during manufacture. As a result, with a synthetic magnetic field produced by an ordinary write current, writing cannot be done, or erroneous writing, such as easy inversion of the information in an unselected MTJ element, is liable to take place. It has been described that use of three types of write lines can increase resistance to erroneous writing.
In addition, U.S. Pat. No. 6,552,579B2 discloses that a magnetic field produced by a bit line not perpendicular to a digit line (or write word line) is applied to an MTJ element.
However, neither U.S. Pat. No. 6,714,445B2 nor U.S. Pat. No. 6,552,579B2 discloses how to configure of a cell array using write lines extending diagonally with respect to the MTJ elements, to arrange the source/sink circuits for the diagonal write lines, and to decode the diagonal write lines.